... those ships were planned with commerce war in mind, therefore diesel engines were selected instead of the usual high pressure steam engine used by the German navy in those days.

This seems rather odd to me if possible. For one thing the H class battleships look like a fair amount of over kill for commerce raiding. So any idea where this came from? Was it the main factor or were the Germans disenchanted with their high pressure systems already and this was an excuse or at only part of the rational?

Commerce raiding is a mission for most warships from historical times. The question is was this mission important enough on it's own for the H-class to dictate their choice of propulsion systems. That it might be a factor is quite reasonable but the quote makes it sound like the sole rational for chooseing the diesel over the high pressure steam system was commerce raiding.

German battleships were designed to fight other battleships. That the ones completed were committed to commerce warfare was the result of the Kriegsmarine being too weak to seek a classic sea superiority naval confrontation against the enemies it eventually had to fight. It is rather like taking a Holland and Holland 450 #2 nitro express elephant rifle to hunt squirrels with--you can do it if it's all you happen to have, but the H&H is more powerful and costly for the purpose.

Their shoulders held the sky suspended;
They stood and Earth's foundations stay;
What God abandoned these defended;
And saved the sum of things for pay.

I looked in Garzke´s. He says that the propulsion was chosen because it was asumed that the ships would have to travel many miles (from North Sea to the Altantic via north of England) before reaching operational ground, be it for commerce raiding or other missions.

lwd wrote:
This seems rather odd to me if possible. For one thing the H class battleships look like a fair amount of over kill for commerce raiding. So any idea where this came from? Was it the main factor or were the Germans disenchanted with their high pressure systems already and this was an excuse or at only part of the rational?

''Commerce raiding'' as I understand from the Z Plan was a strategy for defeating Britain by battleship attack on heavily escorted convoys (not single unescorted merchant ships) in which the escorts would be destroyed and the RN worn down by attrition. The use of diesels was to give the battleships the range and endurance for Atlantic as opposed to North Sea operation.

It bears repeating that German design does not necessarily mesh with any viable, real-world mission, and that ships were built without any specified role.
Bismarck was overkill as a raider. Was that what she was intended for? No one knows.
The reversion to diesel propulsion might be seen as a return to sanity, since the switch to turbines in Scharnhorst (or more precisely, in Ship D) marks a disconnect between mission and capability (turbines on a raider). And yet the sanity had only a partial grip, as "H" was intended to break out into the ocean in company with an aircraft carrier. "H" has twice the range of the turbine-powered Graf Zeppelin, and which ship is going to burn through its fuel faster? (Answer: the one that has to accelerate every time it performs air ops.)
But in any case, "H" was supposed to hunt merchants and fight battleships. No comments are required from me on the practicality of this role.

lwd wrote:In theory shouldn't the mission be defined before they are designed rather than after they are built?

Yes, but here we are dealing with a Fuhrer whose ''destiny is defined in the stars'' and strategy is a concept beyond his understanding. It is the logic of designing battleships to fight other battleships - and then ordering them to avoid battle because any loss incurred in battle is detrimental to national prestige - typical politician, facing both ways.

Well he was the Supreme Commander of all the armed forces in the Third Reich. He wanted a big navy with big battleships. He inspired and approved the Z Plan. And he endorsed the ''take no risks'' policy of the KM for its big ships.